The present invention relates to novel therapeutic methods and pharmaceutical compositions for treating and preventing neurodegenerative processes and, more particularly, to compositions comprising and methods utilizing tellurium-containing compounds for treating and preventing neurodegenerative processes caused by trauma, such as stroke, accident or surgery, substance abuse, disease, such as neurodegenerative disease and the like.
Neurotrophic factors are proteins which are responsible for the growth and survival of neurons during development, and for maintaining adult neurons. Neurotrophic factors are also capable of promoting regrowth of damaged neurons in vitro and in animal models. The possibility of treating degenerative diseases with neurotrophic factors has motivated research for dopaminotrophic factors. Several neurotrophic factors, such as basic fibroblast growth factor (bFGF), epithelial growth factor (EGF), insulin-like growth factor (IGF), and brain-derived neurotrophic factor (BDNF), have shown promise in the rescue of dopaminergic neurons in vitro. However, their effectiveness in vivo has been for the most part somewhat less promising. Neurotrophic factors often cannot reach their target receptors since they rapidly degrade in the blood stream and cannot pass through cell membranes or the blood brain barrier. Alternatively, glial-derived neurotrophic factor (GDNF) has been found to specifically enhance the survival of midbrain dopaminergic neurons in vitro and exert a protective effect on degenerating dopaminergic neurons in vivo. Similarly, insulin-like growth factor 1 (IGF-1) has been found to prevent brain cells from dying after an asphyxial or ischemic brain insult.
Evidence now shows that some drugs can stabilize, reinforce or even regenerate neurotubules within the central or peripheral neurons of a human nervous system. Certain drugs, such as brimonidine and various beta-adrenergic blocking agents, have been accepted as neuroprotective drugs that can protect the central nervous system from acute ischemia and crush trauma in humans. While certain methods and chemical compositions have been developed which aid in inhibiting, remitting, or controlling neurodegeneration, new neuroprotective methods and pharmacotherapeutic agents which are able to slow or stop such neurological damage are needed. There is a great need for additional compounds useful in treating a variety of neurological conditions.
Neurodegenerative processes are generally characterized by the long-lasting course of neuronal death and the selectivity of the neuronal population or brain structure involved in the lesion. The reasons for such specificity are largely unknown, as are the general mechanisms of the diseases. One common feature of these diseases, however, is that neuronal death is thought to involve apoptosis, at least in part.
Neuronal apoptosis is a programmed cell death mechanism, which is required for normal development of the nervous system, but which also occurs in pathological states. Extensive cell death is observed after acute brain injury, including stroke and trauma, and is thought to contribute to neurodegenerative diseases such as Parkinson's disease and Alzheimer's. Cerebral infarctions such as cerebral thrombosis and embolism are triggered by ischemia of the brain due to stenosis of blood vessels, brain thrombi or brain emboli. Treatment consists of anti-edema agents, such as mannitol, which improve post-ischemic cerebral edema; and thrombolytic agents, such as alteplase or urokinase, which do not effect neuronal death or exert a neuroprotective effect. In Parkinson's disease, there is selective degeneration of dopaminergic neurons in the nigrostriatal pathway. Treatment with L-dopa does not arrest progress of the disorder in dopaminergic neurons. Pharmacotherapeutic agents are needed to prevent apoptosis or death of the dopaminergic neurons in Parkinson's disease. Similarly, in Alzheimer's disease, a neurodegenerative disease characterized by the deposition of amyloid senile plaques, neurofibrillary tangle formation and cerebrum atrophy, apoptosis is involved in the mechanism of neuronal death in dementia in these patients. Pharmacotherapeutic agents are generally held to have little efficacy in Alzheimer's dementia.
The neurotrophin family of soluble peptide factors is required for the correct development and differentiation of the nervous system. Neutrotrophins bind receptor tyrosine kinases and activate a variety of intracellular signaling molecules which are necessary for neuron survival and differentiation.(Ebadi M., Bashir R. M., Heidrick M. L. et al, 30 Neurochem Int. 347 [1997]). The identification of the specific molecules involved in vivo has attracted considerable attention. Due to the relative difficulty of studying signaling in neurons, neurotrophin signaling has been primarily studied using the pheochromocytoma PC12 cells as a model system. This cell line has proved useful for studying mechanisms of neuronal survival, differentiation, and cell death. PC12 cells respond to NGF exposure by differentiating to resemble sympathetic neurons. Upon NGF exposure, PC12 cells cease division, extend neuritis, become electrically excitable and express neuronal markers. Withdrawal of trophic support, either by serum deprivation of proliferating neuroblast-like PC12 cells or by NGF/serum removal from neuronally differentiated cells, leads to their apoptotic death. NGF withdrawal similarly triggers death of sympathetic neurons both in vivo and in vitro.
Two signaling cascades have so far been implicated as being involved in the differentiation and survival of PC12 cells upon binding of neurotrophin: activation of the ras/erk pathway (Nakamura, T., Sanokawa, R., Sasaki, Y., et al., 13 Oncogene 1111 [1996]) and P13 Kinase/Rac signaling (Raffioni, S., Bradshaw, R. A., 89 Proc. Natl. Acad. Sci. 9121 [1992]).
The ras/erk signaling pathway appears to be extremely important in mediating NGF-induced differentiation of PC12 cells. Both ras and its signaling intermediates raf, mek and erk kinases are critical for this activity (Cowley, S., Patterson, H., Kemp, P. et al., 77 Cell 841 [1994]). This has been demonstrated by studies showing NGF independent differentiation of PC12 cells expressing constitutively active forms of these intermediates, or inhibition of NGF-induced differentiation by expression of their dominant interfering forms. The erk pathway has been implicated in NGF-mediated PC12 cell survival (Xia, Z., Dickens, M., Raingeaud, J. et al., 270 Science 1326 [1995]), and seems to be required for NGF mediated cell cycle arrest. Protection of neuronal cells from death evoked by withdrawal of trophic support by agents such as N-acetyl cysteine has been shown to be mediated by the activation of the ras/erk pathway, and not by their antioxidative properties. In response to loss of trophic support, PC12 and other cell types show an increased JUN kinase (JNK) activity. Evidence has been provided with PC12 cells that this increase is required for death, and a model has been proposed in which survival occurs when the elevation of JNK activity is suppressed and erk kinase activity is stimulated (Id.). JNK/p38 activates the ICE proteases, thereby leading to apoptotic cell death. Previous studies have shown that multiple molecules prevent the death of naive and neuronal PC12 cells deprived of trophic support. Bc12 has been shown to protect assorted cell types from death evoked by various stimuli. In particular, this protein suppresses death of PC12 cells and sympathetic neurons induced by withdrawal of trophic support, probably via inhibition of JNK and suppression of cytochrome c release from mitochondria, followed by inhibition of caspases. It therefore follows that interference with one or more of the signaling molecules that participate in the pathways that lead to apoptotic death will confer protection from loss of trophic support or other stress conditions.
One of the causes of neurodegenerative disorder is trauma, such as for example, spinal cord injury. Nerve cells of the central nervous system (CNS) i.e., the brain and spinal cord respond to insults differently from most other cells of the body, including those in the peripheral nervous system. The brain and spinal cord are confined within bony cavities that protect them, but also render them vulnerable to compression damage caused by swelling or forceful injury. Cells of the CNS have a very high rate of metabolism and rely upon blood glucose for energy. The “safety factor,” that is the extent to which normal blood flow exceeds the minimum required for healthy functioning, is much smaller in the CNS than in other tissues. For these reasons, CNS cells are particularly vulnerable to reductions in blood flow (ischemia). Other unique features of the CNS are the “blood-brain-barrier” and the “blood-spinal-cord barrier.” These barriers, formed by cells lining blood vessels in the CNS, protect nerve cells by restricting entry of potentially harmful substances and cells of the immune system. Trauma may compromise these barriers, perhaps contributing to further damage in the brain and spinal cord. The blood-spinal-cord barrier also prevents entry of some potentially therapeutic drugs. Finally, in the brain and spinal cord, the glia and the extracellular matrix (the material that surrounds cells) differ from those in peripheral nerves. Each of these differences between the PNS and CNS contributes to their different responses to injury.
In addition to the initial injury involved in damage to the spinal cord following g trauma, delayed, secondary damage occurs. One of the main contributing factors involved in such secondary damage is cell death, either by necrosis or apoptosis. Furthermore, it is believed that the immune system also plays a role in the neurodegeneration resulting from CNS trauma NIH Workshop: Spinal Cord Injury, September 1996. Most types of immune cells enter the CNS only rarely unless it has been damaged by trauma or disease. Microglial cells, which are normally found in the CNS, have some immune functions and become activated in response to damage. Following trauma, other types of immune cells react to signals from damaged tissue and changes in endothelial cells by entering the CNS. Neutrophils are the first type of immune cells to enter the CNS from the rest of the body. These cells enter the spinal cord within about 12 hours of injury and are present for about a day. About 3 days after the injury, T-cells enter the CNS. The key types of immune cells in spinal cord injury appear to be macrophages and monocytes, which enter the CNS after the T-cells. These cells scavenge cellular debris. One type of macrophage, the perivascular cell, may also mediate damage to the endothelial cells that line blood vessels. It is not clear which signals control the entry of immune cells into the CNS, but changes in cell adhesion molecules most likely play an important role.
The action of immune cells once they enter the damaged spinal cord is poorly understood. Some cells engulf and eliminate debris as they do during inflammation in other parts of the body. Macrophages, monocytes, and microglial cells release a host of powerful regulatory substances that may help or hinder recovery from injury. Potentially beneficial substances released by these cells include the cytokines TGF-beta and GM-CSF (transforming growth factor-beta and granulocyte-macrophage colony-stimulating factor) and several other growth factors. Apparently detrimental products include cytokines such as TNF-alpha and IL-1-beta (tumor necrosis factor-alpha and interleukin-1-beta) and chemicals such as superoxides and nitric oxide that may contribute to oxidative damage. Again, it is unclear what is helpful and harmful about many of these powerful substances in the context of the injured spinal cord.
Use of methylprednisolone, Naloxone or Tirilazad has been reported for treatment of damage caused by spinal cord trauma. Known side-effects of methylprednisolone include allergic reaction, which may result in breathing difficulties, closing of the throat, swelling of the lips, tongue or face, or hives; increased blood pressure, resulting in severe headache or blurred vision, and sudden weight gain. Side-effects of naloxone include allergic reaction, as for methylprednisolone; chest pain or fast irregular heartbeats; seizures, difficulty breathing; and fainting.
Various tellurium compounds, having immunomodulating properties, have been shown to have beneficial effects in diverse preclinical and clinical studies. A particularly effective family of tellurium-containing compounds is taught, for example, in U.S. Pat. Nos. 4,752,614; 4,761,490; 4,764,461 and 4,929,739, whereby another effective family is taught, for example, in a recently filed U.S. Provisional Patent Application No. 60/610,660, which are all incorporated by reference as if fully set forth herein. The immunomodulating properties of this family of tellurium-containing compounds is described, for example, in U.S. Pat. Nos. 4,962,207, 5,093,135, 5,102,908 and 5,213,899, which are all incorporated by reference as if fully set forth herein.
One of the most promising compounds described in these patents is ammonium trichloro(dioxyethylene-O,O′)tellurate, which is also referred to herein and in the art as AS101. AS101, as a representative example of the family of tellurium-containing compound discussed hereinabove, exhibits antiviral (Nat. Immun. Cell Growth Regul. 7(3):163-8, 1988; AIDS Res Hum Retroviruses. 8(5):613-23, 1992), and tumoricidal activity (Nature 330(6144):173-6, 1987; J. Clin. Oncol. 13(9):2342-53, 1995; J Immunol. 161(7):3536-42, 1998.
It has been suggested that AS101, as well as other tellurium-containing immunomodulators, stimulate the innate and acquired arm of the immune response. For example, it has been shown that AS101 is a potent activator of interferon (IFN) (IFN) in mice (J. Natl. Cancer Inst. 88(18):1276-84, 1996) and humans (Nat. Immun. Cell Growth Regul. 9(3):182-90, 1990; Immunology 70(4):473-7, 1990; J. Natl. Cancer Inst. 88(18):1276-84, 1996.)
It has also been demonstrated that AS101, as well as other tellurium-containing immunomodulators, induce the secretion of a spectrum of cytokines, such as IL-1, IL-6 and TNF-α, and that macrophages are one main target for AS101 (Exp. Hematol. 23(13):1358-66, 1995) and it was found to inhibit IL-10 at the m-RNA level, and this inhibition may cause an increase in IL-12 (Cell Immunol. 176(2):180-5, 1997); J. Natl. Cancer Inst. 88(18):1276-84, 1996).
Other publications describing the immunomodulation properties of AS101 include, for example, “The immunomodulator AS101 restores T(H1) type of response suppressed by Babesia rodhaini in BALB/c mice”. Cell Immunol 1998 February; “Predominance of TH1 response in tumor-bearing mice and cancer patients treated with AS101”. J Natl Cancer Inst 1996 September; “AS-101: a modulator of in vitro T-cell proliferation”. Anticancer Drugs 1993 June; “The immunomodulator AS101 administered orally as a chemoprotective and radioprotective agent”. Int J Immunopharmacol 1992 May; “Inhibition of the reverse transcriptase activity and replication of human immunodeficiency virus type 1 by AS 101 in vitro”. AIDS Res Hum Retroviruses 1992 May; “Immunomodulatory effects of AS101 on interleukin-2 production and T-lymphocyte function of lymphocytes treated with psoralens and ultraviolet A”. Photodermatol Photoimmunol Photomed 1992 February; “Use and mechanism of action of AS101 in protecting bone marrow colony forming units-granulocyte-macrophage following purging with ASTA-Z 7557”. Cancer Res 1991 Oct. 15; “The effect of the immunomodulator agent AS101 on interleukin-2 production in systemic lupus erythematosus (SLE) induced in mice by a pathogenic anti-DNA antibody”. Clin Exp Immunol 1990 March; “Toxicity study in rats of a tellurium based immunomodulating drug, AS-101: a potential drug for AIDS and cancer patients”. Arch Toxicol 1989; “The biological activity and immunotherapeutic properties of AS-101, a synthetic organotellurium compound”. Nat Immun Cell Growth Regul 1988; and “A new immunomodulating compound (AS-101) with potential therapeutic application”. Nature 1987 November.
In addition to its immunomodulatory effect, AS101 is also characterized by low toxicity. Toxicity tests have shown that LD50 values in rats following intravenous and intramuscular administration of AS101 are 500-1000 folds higher than the immunologically effective dose.
While the immunomodulating effect of tellurium-containing compounds was studied with respect to various aspects thereof, the use of tellurium compounds in the treatment and prevention of neurodegenerative processes has never been suggested nor practiced hitherto.